| Summary: | 碩士 === 國立中山大學 === 材料與光電科學學系研究所 === 104 === Abstract
The aim of this thesis is to understand the reason for the significant different of the tensile behavior of a cold-rolled medium Mn steel after different annealing temperatures. Hot-rolled medium Mn steel is heated at 725oC, then furnace cooled to room temperature. After cold rolling, the medium Mn steel is intercritically annealed at three different temperatures then air cooled to room temperature. Tensile tests were carried out on the specimens with different annealing temperatures, and it was found that annealing temperature strongly affects the tensile behavior and microstructures of theses specimens. Tensile deformation of the specimens annealed at 675℃ was found caused by the deformation of ferrite grains, while strain-induced martensitic transformation was found occurred in the specimens annealed at 700℃, showing TRIP-aided effect. Due to the low stability of austenite, stress-induced martensite was formed in the early stage of tensile test in the specimens annealed at 750℃, which resulted in a very high work hardening rate and poor elongation.
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